notes: surface area of right prisms and cylinders · surface area. the height is half the radius,...

15
Notes: Surface Area of Right Prisms and Cylinders

Upload: others

Post on 27-May-2020

1 views

Category:

Documents


0 download

TRANSCRIPT

Page 1: Notes: Surface Area of Right Prisms and Cylinders · surface area. The height is half the radius, or 6 cm. L = 2 rh = 2 (12)(6) = 144 cm2 S = L + 2 r2 = 144 + 2 (12)2 = 432 in2 Lateral

Notes: Surface Area of Right Prisms and Cylinders

Page 2: Notes: Surface Area of Right Prisms and Cylinders · surface area. The height is half the radius, or 6 cm. L = 2 rh = 2 (12)(6) = 144 cm2 S = L + 2 r2 = 144 + 2 (12)2 = 432 in2 Lateral

Prisms and cylinders have 2 congruent parallel bases.A lateral face is not a base. The edges of the base are called base edges. A lateral edge is not an edge of a base. The lateral faces of a right prism are all rectangles.

A. Definitions and Vocabulary

Page 3: Notes: Surface Area of Right Prisms and Cylinders · surface area. The height is half the radius, or 6 cm. L = 2 rh = 2 (12)(6) = 144 cm2 S = L + 2 r2 = 144 + 2 (12)2 = 432 in2 Lateral

An altitude of a prism or cylinder is a perpendicular segment joining the planes of the bases. The height of a three-dimensional figure is the length of an altitude. For a right prism, the altitude is the same as the length of a lateral side.

Surface area is the total area of all faces and curvedsurfaces of a three-dimensional figure. The lateralarea of a prism is the sum of the areas of the lateral faces.

Page 4: Notes: Surface Area of Right Prisms and Cylinders · surface area. The height is half the radius, or 6 cm. L = 2 rh = 2 (12)(6) = 144 cm2 S = L + 2 r2 = 144 + 2 (12)2 = 432 in2 Lateral

The net of a right prism can be drawn so that the lateral faces form a rectangle with the same height as the prism. The base of the rectangle is equal to the perimeter of the base of the prism.

Page 5: Notes: Surface Area of Right Prisms and Cylinders · surface area. The height is half the radius, or 6 cm. L = 2 rh = 2 (12)(6) = 144 cm2 S = L + 2 r2 = 144 + 2 (12)2 = 432 in2 Lateral

The surface area of a right rectangular prism with length ℓ, width w, and height h can be written as S = 2ℓw + 2wh + 2ℓh.

II. Lateral and Surface Area of Right Prisms

Page 6: Notes: Surface Area of Right Prisms and Cylinders · surface area. The height is half the radius, or 6 cm. L = 2 rh = 2 (12)(6) = 144 cm2 S = L + 2 r2 = 144 + 2 (12)2 = 432 in2 Lateral

Ex 1a. Find the lateral area and surface area of the right rectangular prism. Round to the nearest tenth, if necessary.

L = Ph

= 32(14) = 448 ft2

S = Ph + 2B

= 448 + 2(7)(9) = 574 ft2

P = 2(9) + 2(7) = 32 ft

Page 7: Notes: Surface Area of Right Prisms and Cylinders · surface area. The height is half the radius, or 6 cm. L = 2 rh = 2 (12)(6) = 144 cm2 S = L + 2 r2 = 144 + 2 (12)2 = 432 in2 Lateral

Ex 1b. Find the lateral area and surface area of a right regular triangular prism with height 20 cm , base edges of

length 10 cm, and base area of 𝟐𝟓 𝟑cm2. Round to the nearest tenth, if necessary.

L = Ph

= 30(20) = 600 ft2

S = Ph + 2B

P = 3(10) = 30 cm

The base area is

Page 8: Notes: Surface Area of Right Prisms and Cylinders · surface area. The height is half the radius, or 6 cm. L = 2 rh = 2 (12)(6) = 144 cm2 S = L + 2 r2 = 144 + 2 (12)2 = 432 in2 Lateral

Ex 1c. Find the lateral area and surface area of a cube with edge length 8 cm.

L = Ph

= 32(8) = 256 cm2

S = Ph + 2B

= 256 + 2(8)(8) = 384 cm2

P = 4(8) = 32 cm

Page 9: Notes: Surface Area of Right Prisms and Cylinders · surface area. The height is half the radius, or 6 cm. L = 2 rh = 2 (12)(6) = 144 cm2 S = L + 2 r2 = 144 + 2 (12)2 = 432 in2 Lateral

The lateral surface of a cylinder is the curved surface that connects the two bases. The axis of a cylinder is the segment with endpoints at the centers of the bases. The axis of a right cylinder is perpendicular to its bases. The altitude of a right cylinder is the same length as the axis.

III. Right Cylinders

Page 10: Notes: Surface Area of Right Prisms and Cylinders · surface area. The height is half the radius, or 6 cm. L = 2 rh = 2 (12)(6) = 144 cm2 S = L + 2 r2 = 144 + 2 (12)2 = 432 in2 Lateral
Page 11: Notes: Surface Area of Right Prisms and Cylinders · surface area. The height is half the radius, or 6 cm. L = 2 rh = 2 (12)(6) = 144 cm2 S = L + 2 r2 = 144 + 2 (12)2 = 432 in2 Lateral

Ex 2a. Find the lateral area and surface area of the right cylinder. Give your answers in terms of .

L = 2rh = 2(8)(10) = 160 in2

The radius is half the diameter, or 8 ft.

S = L + 2r2 = 160 + 2(8)2

= 288 in2

Page 12: Notes: Surface Area of Right Prisms and Cylinders · surface area. The height is half the radius, or 6 cm. L = 2 rh = 2 (12)(6) = 144 cm2 S = L + 2 r2 = 144 + 2 (12)2 = 432 in2 Lateral

Ex 2b: Find the lateral area and surface area of a right cylinder with circumference 24 cm and a height equal to half the radius. Give your answers in terms of .

Step 1 Use the circumference to find the radius.

C = 2r Circumference of a circle

24 = 2r Substitute 24 for C.

r = 12 Divide both sides by 2.

Page 13: Notes: Surface Area of Right Prisms and Cylinders · surface area. The height is half the radius, or 6 cm. L = 2 rh = 2 (12)(6) = 144 cm2 S = L + 2 r2 = 144 + 2 (12)2 = 432 in2 Lateral

Step 2 Use the radius to find the lateral area and surface area. The height is half the radius, or 6 cm.

L = 2rh = 2(12)(6) = 144 cm2

S = L + 2r2 = 144 + 2(12)2

= 432 in2

Lateral area

Surface area

Ex 2c. Find the lateral area and surface area of a right cylinder with circumference 24 cm and a height equal to half the radius. Give your answers in terms of .

Page 14: Notes: Surface Area of Right Prisms and Cylinders · surface area. The height is half the radius, or 6 cm. L = 2 rh = 2 (12)(6) = 144 cm2 S = L + 2 r2 = 144 + 2 (12)2 = 432 in2 Lateral

Ex 2d. Find the lateral area and surface area of a cylinder with a base area of 49 and a height that is 2 times the radius.

Step 1 Use the circumference to find the radius.

A = r2

49 = r2

r = 7

Area of a circle

Substitute 49 for A.

Divide both sides by and take the square root.

Page 15: Notes: Surface Area of Right Prisms and Cylinders · surface area. The height is half the radius, or 6 cm. L = 2 rh = 2 (12)(6) = 144 cm2 S = L + 2 r2 = 144 + 2 (12)2 = 432 in2 Lateral

Step 2 Use the radius to find the lateral area and surface area. The height is twice the radius, or 14 cm.

L = 2rh = 2(7)(14)=196 in2

S = L + 2r2 = 196 + 2(7)2 =294 in2

Lateral area

Surface area

Ex 2e. Find the lateral area and surface area of a cylinder with a base area of 49 and a height that is 2 times the radius.